**1.4. Biology, population state and trends**

154 New Approaches to the Study of Marine Mammals

**1.3. Local geographical distribution** 

1984, 1987).

(www.freplata.org).

medicines and aphrodisiacs (Acosta y Lara, 1884; DINARA, 2006; Pérez Fontana, 1943;

Harvesting and slaughtering of Uruguayan seals stopped in 1978 for South American sea lions and in 1991 for South American fur seals. From 1992 to the present day, the conservation and preservation of pinnipeds and cetacean species are under control of the National Direction

Uruguayan South American fur seal and sea lion colonies are located on three main islands in the Atlantic Ocean: 1) Isla de Lobos and Lobos Islet, 9,260 m off Punta del Este (Department of Maldonado); 2) Torres Group Islands (Rasa Island, Encantada Island and Islet) close to Polonio's Cape (Department of Rocha) and 3) Marco Island close to Valizas (Department of Rocha). There are two more small islets close to La Coronilla (Department of Rocha), where small groups of sea lions aggregate in reproductive areas (Fig. 4). Sometimes, a few South American fur seals also appear on these islands (Ponce de León, 2000; Ponce de León & Pin, 2006; Smith, 1934; Vaz Ferreira, 1950, 1952, 1956; Vaz Ferreira & Ponce de León,

**Figure 4.** Location of Uruguayan South American fur seal and sea lion calving, breeding and mating islands close to the shorelines of the Departments of Maldonado and Rocha : Isla de Lobos (35º 01' 38" S – 54º 52' 55" W) and Lobos Islet; Rasa Island (34º 24' 12" S – 53º 46' 10" W), Encantada Island (34º 24' 26" S – 53º 45' 56" W), Torres Islet (34º 24' 09" S – 53º 44' 59" W); Marco Island (34º 20' 59" S – 53º 44' 26" W); 3) Verde Island and Coronilla's Islet (33º 56' 21" S – 53º 29' 15" W). Isobath data layer obtained from

FREPLATA-Proyecto de Protección Ambiental del Río de la Plata y su Frente Marítimo

Ponce de León, 2000; Vaz-Ferreira 1982; Vaz-Ferreira & Ponce de León, 1984, 1987).

of Aquatic Resources (DINARA: Dirección Nacional de Recursos Acuáticos).

Parturition and mating occur between November and January for South American fur seals and during January and February for South American sea lions (Franco-Trecu, 2005; Ponce de León, 2000, 2001; Ponce de León & Pin, 2006; Trimble, 2008). Gestation lasts around one year. In South American fur seals, lactation extends for several months and weaning begins between the 8th and the 12th month of age (Ponce de León, 1983, 1984, 2000; Ponce de León & Pin, 2006). From the 6th month of age, pups start eating fish and small mollusks as can be seen when analyzing stomach contents and gastrointestinal parasites of indirect cycle (Katz et al., 2012; Morgades et al., 2006). In some cases, South American fur seal lactation can be extended further, and the mother has to feed two pups from two consecutive breeding seasons: the yearling pup and the new one (Vaz-Ferreira & Ponce de León, 1987). In sea lions, there is a mother-pup relation for one year and in some cases for two (Vaz-Ferreira & Achaval, 1979) or possibly, up to three years (Soto, 1999). Little is known about the exact time of weaning, and whether pups are mixing milk with solid prey. It was suggested that weaning occurs when the mother actively rejects the older pup because a new one is born (Vaz-Ferreira, 1981; Vaz-Ferreira & Achaval, 1979).

South American fur seals have a lek reproductive system (Franco-Trecu, 2005). During the reproductive season, males fight each other to defend territories in very violent battles that can result in serious wounds and scars (Ponce de León, 2000; Ponce de León & Pin, 2006; Vaz-Ferreira, 1976, 1982; Vaz-Ferreira & Ponce de León, 1984, 1985, 1987). Females have no strong bonds with the areas defended by males. Fur seal colonies on islands are occupied by individuals from different age classes during the entire year. During the reproductive season there is a high density of animals in rocky areas as compared to sandy surfaces. As a consequence of the high environmental temperature, territorial males may abandon the reproductive areas in order to refresh themselves in the water (Vaz-Ferreira & Palerm, 1962; Vaz-Ferreira & Sierra de Soriano, 1962). After giving birth, South American fur seal females may remain with their pups for 6 to 11 days (Franco-Trecu, 2010) before starting short foraging trips that gradually become longer as the pups grow bigger and more independent (Ponce de León & Pin, 2006; Franco-Trecu, 2010).

The Uruguayan South American fur seal population is the biggest in South America (Vaz-Ferreira, 1982), with an annual growth rate of 3.3% (Páez, 2006) and an actual size estimated at 400,000 individuals. However, this species is included by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in the list of globally protected species because of population decline of other South American colonies (de Oliveira et al., 2006). For the International Union for Conservation of Nature (IUCN) the same species is listed as "Of low concern".

South American sea lions have a polygynous breeding system (Ponce de Leon & Pin, 2006; Trimble, 2008; Vaz-Ferreira, 1981; Vaz-Ferreira & Sierra de Soriano, 1962). The reproductive season extends from mid December to mid February. During this time males fight each other to establish territories and to defend females from other males (Campagna & Le Boeuf, 1988; Ponce de Leon & Pin, 2006). Pregnancy has an estimated duration of 363 days (Franco-

Trecu & Trimble, unpublished data). Territorial males display violent fights that may last at least one hour, and end with serious wounds. After parturition, sea lion females remain with their pups in order to suckle them for approximately one week and then start short foraging trips of three days, alternated with two-day suckling periods on land (Campagna & Le Boeuf, 1988). There is a decrease in the number of adult males and females at the end of the reproductive season because, after fasting during the breeding season, males begin their foraging period at sea. In addition, adult females alternate foraging trips at sea and suckling periods ashore, and move to other areas of the island (Franco-Trecu & Trimble, unpublished data; Ponce de León & Pin, 2006). Despite the fact that sea lions abandon the islands in order to move to feeding areas, there are generally some animals in the rookeries, even outside the reproductive season. In many other South American colonies this species maintains an increasing population growth (Grandi et al., 2008; Sepúlveda et al., 2006) and has been classified as low risk by the IUCN. However, sea lions in Uruguay are considered a highly endangered species due to their population decrease of 1.7 to 2% annually, with a total population estimated at only 12.000 individuals (Páez, 2006; Pedraza et al., 2009).

Uruguayan Pinnipeds (*Arctocephalus australis* and *Otaria flavescens*): Evidence of Influenza Virus and *Mycobacterium pinnipedii* Infections 157

squid (*Illex argentinus, Loligo sanpaulensis*), hake (*Merluccius hubbsi*), striped weakfish (*Cynoscion guatucupa*), oceanic shrimp (*Pleoticus muelleri)* and cutlassfish (*Trichiurus lepturus*) (Frau & Franco-Trecu, 2010; Naya et al., 2002; Pin et al., 1996; Ponce de León et al., 1988; Ponce de León et al., 2000; Ponce de León & Pin, 2006; Vaz Ferreira 1976; Vaz-Ferreira & Ponce de León, 1984, 1987). Uruguayan fur seals usually do not interfere directly with artisanal and industrial fisheries, as they do not eat from nets nor destroy fishing gears (Ponce de León & Pin, 2006), though there are a few records of fur seal by-catch in artisanal

Diving records obtained by different researchers showed that during lactation, female fur seals perform dives of up to 186 m (media: 23.5 m ± 19.5 m) in depth with an average duration of 1.2 min ± 0.8 min (max. 5.3 min.) (Riet et al., 2010; York et al., 1998). These data suggest that females use both benthic and pelagic foraging strategies, and demonstrate their huge endurance for deep dives, apnea resistance and swimming ability. Diurnal dives were shallower and shorter than nocturnal ones (Riet et al., 2010). It was determined that lactating females consume different prey species, adapting their diving strategies to variations in food resources (Ponce de León & Páez, 1996; Ponce de León & Pin, 2006; Riet et al., 2010; York et

During early lactation, female sea lions perform dives of 21 m ± 8 m in depth with an average time of 1.9 min ± 0.7 min. Mean distance traveled per trip was 62.2 km ± 63.0 km. Foraging trips lasted 1.3 ± 0.8 days and did not exceed the continental shelf (>50 m of depth). Maximum distance from the colony was 98.60 km ± 31.3 km. These results indicate that during the breeding season females forage in coastal and shallow continental shelf areas (Riet et al., 2009, 2012). In autumn, foraging trips last 5 days (range: 1-14 days). Most animals seemed to complete round trips along the same tracks, meaning that each animal uses the same path on successive trips, with low overlap between individuals. Site fidelity to Lobos Island was highly remarkable for all animals, independently of their reproductive condition

Sea lions compete directly with small-scale coastal fishing and artisanal fisheries, feeding on species that are part of the fishermen's daily catch by stealing prey trapped in nets and longlines, and sometimes causing important damage or cracks in the gear (Franco-Trecu et. al., 2012; Lezama & Szteren, 2003; Ponce de León & Pin, 2006; Szteren & Páez, 2002). According to different authors, the sea lions' diet is mainly made up of coastal prey and some pelagic fishes: whitemouth croaker *(Micropogonias furnieri)*, striped weakfish (*Cynoscion guatucupa*), Brazilian codling (*Urophysis brasiliensis*), cutlassfish (*Trichiurus lepturus*), mackerel (*Trachurus lathami*), Argentinean conger (*Conger orbignyanus*), carangid (*Parona signata*), two species of anchovies (*Engraulis anchoita* and *Anchoa marinii*), and Argentinean croaker (*Umbrina canosai*) (Franco-Trecu, 2010; Naya et al., 2000; Pinedo & Barros, 1983; Ponce de León & Pin, 2006; Riet et al., 2011, 2012; Vaz Ferreira, 1981). As a consequence of interactions with sea lions, fishermen lost prey with high local commercial market value. Sometimes, fishermen find small shark specimens in their nets (*Mustelus schmitti, Galeorhinus galeus, Myliobatis* spp.) which have bite marks in their abdominal area

(Franco-Trecu et al., 2009) and industrial fisheries (Szephegyi et al., 2010).

al., 1998).

(Rodríguez et al., 2012).

On Lobos Island and Lobos Islet, South American sea lion groups are found in small patches, surrounded by large groups of South American fur seals. However, on the Torres Islands (Rasa Island, Encantada Island and Islet), Marco Island and other islets, groups of sea lions are more numerous than on the bigger Lobos Island. According to Pedraza et al., (2009) and Ponce de León (unpublished data), sea lion populations are stable or increasing (2.4% annually) in Polonio´s Cape islands, while in Lobos Island their growth have a negative tendency. This is related to a positive trend in the *A. australis* population and may be an indicator of competition for territory (breeding areas), a process that occurs only on Lobos Island and Lobos Islet.

The breeding and reproductive areas of the elephant seal *Mirounga leonina* are located in sub Antarctic regions along the coast of South America (Campagna & Lewis, 1992; Lewis et al*.,* 1998) and smaller colonies are formed in the Antarctic (Le Boeuf & Laws, 1994). The only large breeding colony of southern elephant seals on the South American continent is found in Península Valdés (42°04'S, 63°45'W) (Campagna & Lewis, 1992; Le Boeuf & Laws 1994; Lewis et al., 2004). Young, juvenile and adult animals migrate to northern regions (Lewis et al., 2006) and occur at different points all along the Uruguayan shoreline of the La Plata River and Atlantic Ocean beaches. During practically the whole year, elephant seals of both sexes are frequently seen in the flat areas of access to Lobos Island, Lobos Islet, Rasa Island and Coronilla Islet (Fig. 3 and 4). Mother and pup couples have been seen on Lobos Island in October, and in some odd cases, individuals have swum up the waters of the Uruguay River to the Departments of Rio Negro and Paysandú (Ponce de León & Pin, 2000).
